Bellwork 2-17-20141. Look at the picture:

1. Which fragment, A, B, or C is smallest?

2. Which fragment is largest?

3. What is the charge of DNA?

4. Based only on your observations…which band, A, B, or C has the largest quantity DNA?

AIMS

In the labGo to the lab and set up your gel box.

The flat side of the black wedge should face inwards.

The comb must go on the negative (black side).

This is different from how we set it up last time!

Raise your hand. A biotechnology student will check your set-up and pour your gel when you group is ready C

OMB

Patient Medical testWe have decided to test the patient and her

family for Huntington’s disease based on our research and the patient’s symptoms.

While the agarose hardens….Problem (write on your lab paper)- Who in the family carries the gene for Huntington’s disease?You have taken a DNA sample from each member of the family: father, mother, daughter, and son.

How can we use these electrodes?

What is DNA’s charge?If DNA is negative, what happens when we turn the electricity on?

How does gel electrophoresis work?

What is Huntington’s disease?The defect responsible for HD is a

small sequence of DNA on chromosome 4 in which several base pairs are repeated many, many times.

The normal gene has three DNA bases, composed of the sequence CAG.

Healthy gene has 10-24 CAG repeats

Huntington’s gene has 37-80 CAG repeats

Will a person with a trait for Huntington’s have a thicker fragment on the gel or a thinner one?

Who will get Huntington’s disease?Huntington’s disease is a dominant disorder

that must be passed down from parent to child

What does it mean to be a dominant trait?

Since Huntington’s disease is dominant…..You only need to inherit one bad copy from

one parent to develop the disease. (remember that you get ½ your DNA from your mother and ½ from you father))

If a trait is recessive how many copies would you need?2

Possible results– copy the image in your notes! Since Huntington’s disease has many more

repeats than the normal genotypes, what would you expect to see on the gel if someone has Huntington’s disease vs. someone who does not?

Remember, there are two traits for the disease so individuals can have three different combinations:

Normal

Huntington’s

Huntington’s

2 recessive traits (smaller)

1 dominant and one recessive(one large, one small)2 dominant traits (both large)

hh - normal

Hh – huntington’s

HH – huntinton’s

Write your hypothesis:Choose a family member(s)…Option 1: If _______ has Huntington's disease, then their gel will have _______ band(s) [describe what the bands will look like]. Option 2: If _______ does not have Huntington's then their gel will have _______ band(s) [describe what their bands will look like].

Make a record of what goes where!!

1. Draw a picture of your gel and indicate where each sample will go (remember there are 8 wells and 5 samples, one sample is a control). M

W M

D A

B

1

2

3

4

5

Daughter

Son

Observations (10 total)Quantitative (numbers) Qualitative (not numbers)

**I suggest someone in your group take a picture on their phone a few times during the process (especially at the end!)

Pipettor/Gel Loading RefresherDo not cross contaminate – one sample per

pipette tip and discard in the beaker!!!Push all the way down, place in sample,

releasePush all the way down to release sample into well Don’t scrap the gel, steady hands!

Load and run YOUR gels!!1. Use the yellow pipettor with a fresh tip to load

each sample exactly according to your lane map.2. Raise your hand to have a biotech student add

the buffer when you are done3. Connect cables and run the gel at 125 volts for 15

minutes. Note the starting time.4. While you wait, make observations and lab notes.

(Note any spills or over flow. Did your pipettor tip puncture the gel? Can you see any thing happen in the box?)

5. While you wait, make another diagram of your gel on which to draw your final results. Make it large enough to record measurements.

How can you see if someone has the gene for Huntington’s disease?A machine is used to copy the DNA at specific

locations. This machine is called a PCR machine. It

allows you to make thousands of copies of a short section of DNA (like a gene) so you can visualize and measure the length of the DNA on a gel.

=

How does Huntington’s disease make you sick?A review of protein synthesis and its application in HD

Remember the central dogma of biology

What amino acid do these codons code for?

AUG

CAU

GUG

GAG

UAG

What does the HD gene do?The short answer- It is unclear. Researchers

are still trying to understand what the Huntington gene does.

The gene is essential for development, and absence of the gene is lethal in mice

Wild type protein (this is the non-disease type)

Why does this mutation make you sick?Over time the mutated gene is copied into

long proteins with extra glutamine amino acids. These fragments can then mis-fold and “stick together” in a process called protein aggregation.

Why do you think it would be harmful to have proteins sticking together?

ResultsThe mom & daughter have bands that are

very far apart, indicating one very large allele.  The father & son have two bands that are very close together, indicating two healthy alleles with slightly different number of repeats.  I just used beads to show my students.

Conclusion Questions:Write in paragraph form…1. Restate your hypothesis.2. What conclusions can you make about EACH

person based on the gel? Give a detailed description of what each person’s gel bands looked like and why they have the disease or why not. Does this support or reject your hypothesis?

3. Based on the patient’s (mom’s) back story, who do you think she inherited the deadly allele from? Why?